Secondary battery

ABSTRACT

A secondary battery includes a rectangular exterior body having an opening and containing a first electrode assembly and a second electrode assembly, a sealing plate sealing the opening, and a positive-electrode current collector. The sealing plate has an electrolytic solution introduction hole. The first electrode assembly includes a first insulating sheet on an outermost surface thereof adjacent to the second electrode assembly. The second electrode assembly includes a second insulating sheet on an outermost surface thereof adjacent to the first electrode assembly. A first tape is attached to both an outermost surface of a first positive-electrode tab group and the first insulating sheet. A second tape is attached to both an outermost surface of a second positive-electrode tab group and the second insulating sheet. At least one of the first tape and the second tape is located to face the electrolytic solution introduction hole.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention application claims priority to Japanese PatentApplication No. 2019-026198 filed in the Japan Patent Office on Feb. 18,2019, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a secondary battery.

Description of Related Art

Driving power sources of, for example, electric vehicles (EVs) andhybrid electric vehicles (HEVs or PHEVs) include a secondary battery,such as an alkaline secondary battery or a nonaqueous electrolytesecondary battery.

A secondary battery includes a battery case constituted by an exteriorbody having the shape of a tube with an opening and a bottom and asealing plate that seals the opening. The battery case contains anelectrode assembly, which includes positive electrode plates, negativeelectrode plates, and separators, together with an electrolyte. Apositive electrode terminal and a negative electrode terminal areattached to the sealing plate. The positive electrode terminal iselectrically connected to the positive electrode plates by apositive-electrode current collector. The negative electrode terminal iselectrically connected to the negative electrode plates by anegative-electrode current collector.

In such a secondary battery, the sealing plate has an electrolyticsolution introduction hole.

Electrolytic solution is introduced into the battery case through theelectrolytic solution introduction hole, and then the electrolyticsolution introduction hole is sealed with a sealing member (JapanesePublished Unexamined Patent Application No. 2018-29006).

BRIEF SUMMARY OF THE INVENTION

An object of the present disclosure is to provide a highly reliablesecondary battery in which short-circuiting between a positive electrodeplate and a negative electrode plate is prevented.

A secondary battery according to an embodiment of the present disclosureincludes a first electrode assembly including a positive electrode plateand a negative electrode plate; a second electrode assembly including apositive electrode plate and a negative electrode plate; an exteriorbody having an opening and containing the first electrode assembly andthe second electrode assembly; a sealing plate sealing the opening; acurrent collector that is closer to the sealing plate than are the firstelectrode assembly and the second electrode assembly; and a terminalelectrically connected to the current collector and attached to thesealing plate. The sealing plate has an electrolytic solutionintroduction hole. The first electrode assembly includes a firstinsulating sheet on an outermost surface thereof adjacent to the secondelectrode assembly. The second electrode assembly includes a secondinsulating sheet on an outermost surface thereof adjacent to the firstelectrode assembly. The first electrode assembly includes a firstelectrode tab group at an end thereof adjacent to the sealing plate, thefirst electrode tab group being electrically connected to the positiveelectrode plate or the negative electrode plate. The second electrodeassembly includes a second electrode tab group at an end thereofadjacent to the sealing plate, the second electrode tab group beingelectrically connected to the positive electrode plate or the negativeelectrode plate. The first electrode tab group and the second electrodetab group are connected to the current collector. A first tape isattached to both the outermost surface of the first tab group and thefirst insulating sheet. A second tape is attached to both the outermostsurface of the second tab group and the second insulating sheet. Atleast one of the first tape and the second tape is located to face theelectrolytic solution introduction hole. The electrolytic solutionintroduction hole is sealed by the sealing member.

When a secondary battery includes an electrode assembly including astacked end portion at which an end portion of a positive electrodeplate, an end portion of a separator, and an end portion of a negativeelectrode plate are disposed and when the stacked end portion isdisposed adjacent to a sealing plate, curling of the separator may occurwhen electrolytic solution is introduced through an electrolyticsolution introduction hole in the sealing plate. When curling of theseparator occurs, the positive electrode plate and the negativeelectrode plate that are adjacent to each other may come into contactwith each other and cause short-circuiting. Also, a portion of apositive-electrode-active-material layer or anegative-electrode-active-material layer may fall and causeshort-circuiting.

According to the configuration of the secondary battery of theembodiment of the present disclosure, the separator can be effectivelyprevented from curling when the electrolytic solution is introducedthrough the electrolytic solution introduction hole in the sealingplate. Therefore, short-circuiting between the positive electrode plateand the negative electrode plate can be effectively prevented.

According to the present disclosure, the separator can be prevented fromcurling when the electrolytic solution is introduced into the batterycase through the electrolytic solution introduction hole in the batterycase. Therefore, a highly reliable secondary battery in whichshort-circuiting between the positive electrode plate and the negativeelectrode plate is prevented can be provided.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view of a rectangular secondary batteryaccording to an embodiment;

FIG. 2 is a sectional view of the rectangular secondary battery takenalong line II-II in FIG. 1;

FIG. 3A is a plan view of a positive electrode plate according to theembodiment;

FIG. 3B is a plan view of a negative electrode plate according to theembodiment;

FIG. 4 is a plan view of an electrode assembly according to theembodiment;

FIG. 5 illustrates a state in which positive-electrode tab groups areconnected to a second positive-electrode current collector andnegative-electrode tab groups are connected to a secondnegative-electrode current collector;

FIG. 6A is an enlarged sectional view of a region including an outermostsurface of a first electrode assembly and a first positive-electrode tabgroup;

FIG. 6B is an enlarged sectional view of a region including an outermostsurface of a second electrode assembly and a second positive-electrodetab group;

FIG. 7 illustrates a surface of a sealing plate facing electrodeassemblies after a first positive-electrode current collector and afirst negative-electrode current collector are attached;

FIG. 8 illustrates the surface of the sealing plate facing the electrodeassemblies after the second positive-electrode current collector isattached to the first positive-electrode current collector and thesecond negative-electrode current collector is attached to the firstnegative-electrode current collector; and

FIG. 9 is a sectional view of the sealing plate 2 taken in a short-sidedirection, illustrating a region including an electrolytic solutionintroduction hole.

DETAILED DESCRIPTION OF THE INVENTION

The structure of a rectangular secondary battery 20 will now bedescribed as a secondary battery according to an embodiment. The presentinvention is not limited to the embodiment described below.

As illustrated in FIGS. 1 and 2, the rectangular secondary battery 20includes a battery case 100 including a rectangular exterior body 1having the shape of a rectangular tube with an opening and a bottom anda sealing plate 2 that seals the opening in the rectangular exteriorbody 1. The rectangular exterior body 1 and the sealing plate 2 arepreferably made of metal. The rectangular exterior body 1 containselectrode assemblies 3, which each include positive electrode plates andnegative electrode plates, together with an electrolyte.

Each electrode assembly 3 includes a positive-electrode tab group 40including a plurality of positive-electrode tabs 4 d and anegative-electrode tab group 50 including a plurality ofnegative-electrode tabs 5 c at an end thereof adjacent to the sealingplate 2. The positive-electrode tab group 40 is electrically connectedto a positive electrode terminal 7 by a second positive-electrodecurrent collector 6 b and a first positive-electrode current collector 6a. The negative-electrode tab group 50 is electrically connected to anegative electrode terminal 9 by a second negative-electrode currentcollector 8 b and a first negative-electrode current collector 8 a. Thefirst positive-electrode current collector 6 a and the secondpositive-electrode current collector 6 b form a positive-electrodecurrent collector 6. The positive-electrode current collector 6 mayinstead be formed of a single component. The first negative-electrodecurrent collector 8 a and the second negative-electrode currentcollector 8 b form a negative-electrode current collector 8. Thenegative-electrode current collector 8 may instead be formed of a singlecomponent.

The first positive-electrode current collector 6 a, the secondpositive-electrode current collector 6 b, and the positive electrodeterminal 7 are preferably made of metal, more preferably aluminum or analuminum alloy. An outer insulating member 10 made of resin is disposedbetween the positive electrode terminal 7 and the sealing plate 2. Aninner insulating member 11 made of resin is disposed between the firstpositive-electrode current collector 6 a and the sealing plate 2 andbetween the second positive-electrode current collector 6 b and thesealing plate 2.

The first negative-electrode current collector 8 a, the secondnegative-electrode current collector 8 b, and the negative electrodeterminal 9 are preferably made of metal, more preferably copper or acopper alloy. The negative electrode terminal 9 preferably includes aportion made of aluminum or an aluminum alloy and a portion made ofcopper or a copper alloy. In this case, preferably, the portion made ofcopper or a copper alloy is connected to the first negative-electrodecurrent collector 8 a, and the portion made of aluminum or an aluminumalloy projects outward beyond the sealing plate 2. An outer insulatingmember 12 made of resin is disposed between the negative electrodeterminal 9 and the sealing plate 2. An inner insulating member 13 madeof resin is disposed between the first negative-electrode currentcollector 8 a and the sealing plate 2 and between the secondnegative-electrode current collector 8 b and the sealing plate 2.

An electrode assembly holder 14 formed of an insulating sheet made ofresin is disposed between the rectangular exterior body 1 and theelectrode assemblies 3. The electrode assembly holder 14 is preferablyformed by folding an insulating sheet made of resin in the shape of abag or a box. The sealing plate 2 has an electrolytic solutionintroduction hole 15. The electrolytic solution introduction hole 15 issealed with a sealing member 16. The sealing member 16 may be a blindrivet. Alternatively, the sealing member 16 may be made of metal andwelded to the sealing plate 2. The sealing plate 2 includes a gasdischarge valve 17 that breaks to enable gas in the battery case 100 tobe discharged from the battery case 100 when the pressure in the batterycase 100 reaches or exceeds a predetermined pressure.

A method for manufacturing the rectangular secondary battery 20 and thestructure of the rectangular secondary battery 20 will now be describedin detail.

Positive Electrode Plate

A method for manufacturing a positive electrode plate will now bedescribed.

Production of Positive-Electrode-Active-Material Layer Slurry

A positive-electrode-active-material layer slurry is produced by mixinga lithium nickel cobalt manganese composite oxide that serves as apositive electrode active material, polyvinylidene fluoride (PVdF) thatserves as a binder, a carbon material that serves as a conductive agent,and N-methyl-2-pyrrolidone (NMP) that serves as a dispersion medium sothat the mass ratio between the lithium nickel cobalt manganesecomposite oxide, PVdF, and the carbon material is 97.5:1:1.5.

Production of Positive-Electrode-Protecting Layer Slurry

A protecting layer slurry is produced by mixing alumina powder, a carbonmaterial that serves as a conductive agent, polyvinylidene fluoride(PVdF) that serves as a binder, and N-methyl-2-pyrrolidone (NMP) thatserves as a dispersion medium so that the mass ratio between the aluminapowder, the carbon material, and PVdF is 83:3:14.

Formation of Positive-Electrode-Active-Material Layers andPositive-Electrode-Protecting Layers

The positive-electrode-active-material layer slurry and thepositive-electrode-protecting layer slurry produced by theabove-described methods are applied to both sides of an aluminum foilhaving a thickness of 15 μm serving as a positive electrode core byusing a die coater. The positive-electrode-protecting layer slurry isapplied in regions near end portions of the regions in which thepositive-electrode-active-material layer slurry is applied to thepositive electrode core.

The positive electrode core to which thepositive-electrode-active-material layer slurry and thepositive-electrode-protecting layer slurry are applied is dried toremove NMP contained in the positive-electrode-active-material layerslurry and the positive-electrode-protecting layer slurry. Thus,positive-electrode-active-material layers and protecting layers areformed. After that, the positive-electrode-active-material layers arecompressed by being passed between a pair of press rollers, so that apositive electrode original plate is formed. A positive electrode plate4 is formed by cutting the positive electrode original plate in apredetermined shape.

FIG. 3A is a plan view of the positive electrode plate 4. The positiveelectrode plate 4 includes an aluminum foil that serves as a positiveelectrode core 4 a and positive-electrode-active-material layers 4 bformed on both sides of the aluminum foil. The positive electrode plate4 includes a positive-electrode tab 4 d at one edge thereof, thepositive-electrode tab 4 d being an exposed portion of the positiveelectrode core 4 a that does not have thepositive-electrode-active-material layers 4 b on both sides thereof. Thepositive electrode plate 4 includes positive-electrode-protecting layers4 c formed on both sides of the positive electrode core 4 a in regionsnear the edge at which the positive-electrode tab 4 d is provided andnear the proximal end of the positive-electrode tab 4 d.

Negative Electrode Plate

A method for manufacturing a negative electrode plate will now bedescribed.

Production of Negative-Electrode-Active-Material Layer Slurry

A negative-electrode-active-material layer slurry is produced by mixinggraphite that serves as a negative electrode active material, styrenebutadiene rubber (SBR) and carboxymethyl cellulose (CMC) that serve as abinder, and water that serves as a dispersion medium so that the massratio between graphite, SBR, and CMC is 98:1:1.

Formation of Negative-Electrode-Active-Material Layers

The negative-electrode-active-material layer slurry produced by theabove-described method is applied to both sides of a copper foil havinga thickness of 8 μm serving as a negative electrode core by using a diecoater.

The negative electrode core to which thenegative-electrode-active-material layer slurry is applied is dried toremove water contained in the negative-electrode-active-material layerslurry. Thus, negative-electrode-active-material layers are formed.After that, the negative-electrode-active-material layers are compressedby being passed between a pair of press rollers, so that a negativeelectrode original plate is formed. A negative electrode plate 5 isformed by cutting the negative electrode original plate in apredetermined shape.

FIG. 3B is a plan view of the negative electrode plate 5. The negativeelectrode plate 5 includes a copper foil that serves as a negativeelectrode core 5 a and negative-electrode-active-material layers 5 bformed on both sides of the copper foil. The negative electrode plate 5includes a negative-electrode tab 5 c at one edge thereof, thenegative-electrode tab 5 c being an exposed portion of the negativeelectrode core 5 a that does not have thenegative-electrode-active-material layers 5 b on both sides thereof

Production of Electrode Assembly

An electrode assembly 3 having a stacked structure is manufactured bystacking positive electrode plates 4 and negative electrode plates 5produced by the above-described method with rectangular separators 90made of polyolefin interposed therebetween. FIG. 4 is a plan view of theelectrode assembly 3. The electrode assembly 3 includes thepositive-electrode tab group 40 at an end thereof, thepositive-electrode tab group 40 being formed by stacking thepositive-electrode tabs 4 d of the positive electrode plates 4. Theelectrode assembly 3 also includes the negative-electrode tab group 50at the end thereof, the negative-electrode tab group 50 being formed bystacking the negative-electrode tabs 5 c of the negative electrodeplates 5. The electrode assembly 3 is flat. The electrode assembly 3 hasthe separators 90 on both outer surfaces thereof in the direction inwhich the positive electrode plates 4, the separators 90, and thenegative electrode plates 5 are stacked.

The electrode assembly 3 may include either a plurality of rectangularseparators or a band-shaped separator that is fan-folded. Alternatively,a band-shaped separator may be wound in the electrode assembly 3. Theseparators may include a base material made of polyolefin and aheat-resistant layer provided on a surface of the base material. Theheat-resistant layer includes inorganic powder, such as ceramic powder,and a binder. The separators may have an adhesive layer on a surfacethereof, and be bonded to the positive electrode plates 4 and/or thenegative electrode plates 5 by the adhesive layer.

The number of positive electrode plates stacked in a single electrodeassembly 3 is not limited, but is preferably 10 to 100, and morepreferably 30 to 80. The number of negative electrode plates included ina single electrode assembly 3 is preferably greater than the number ofpositive electrode plates by one so that both surfaces of each of thepositive electrode plates face the negative electrode plates.

The electrode assembly 3 may instead be a flat-wound electrode assemblyobtained by winding a band-shaped positive electrode plate and aband-shaped negative electrode plate with a band-shaped separatorinterposed therebetween.

Connection Between Current Collectors and Tabs

Two electrode assemblies 3, which will be referred to as a firstelectrode assembly 3 a and a second electrode assembly 3 b, are producedby the above-described method. The positive-electrode tab group 40 andthe negative-electrode tab group 50 of the first electrode assembly 3 awill be respectively referred to as a first positive-electrode tab group40 a and a first negative-electrode tab group 50 a. Thepositive-electrode tab group 40 and the negative-electrode tab group 50of the second electrode assembly 3 b will be respectively referred to asa second positive-electrode tab group 40 b and a secondnegative-electrode tab group 50 b. The first electrode assembly 3 a andthe second electrode assembly 3 b may have completely the same structureor different structures.

As illustrated in FIG. 5, the first positive-electrode tab group 40 a ofthe first electrode assembly 3 a and the second positive-electrode tabgroup 40 b of the second electrode assembly 3 b are connected to thesecond positive-electrode current collector 6 b to form joined portions60. The first negative-electrode tab group 50 a of the first electrodeassembly 3 a and the second negative-electrode tab group 50 b of thesecond electrode assembly 3 b are connected to the secondnegative-electrode current collector 8 b to form joined portions 61. Thejoining method may be, for example, ultrasonic welding (ultrasonicbonding), resistance welding, or laser welding.

As illustrated in FIGS. 5 and 6A, a first outermost separator 90 a,which serves as a first insulating sheet, is provided on an outermostsurface of the first electrode assembly 3 a that is adjacent to thesecond electrode assembly 3 b when the rectangular secondary battery 20is completed. A first tape 80 a is attached to both the first outermostseparator 90 a and the positive-electrode tabs 4 d that form the firstpositive-electrode tab group 40 a. The first tape 80 a may be attachedeither before or after the first positive-electrode tab group 40 a andthe second positive-electrode tab group 40 b are connected to the secondpositive-electrode current collector 6 b.

As illustrated in FIGS. 5 and 6B, a second outermost separator 90 b,which serves as a second insulating sheet, is provided on an outermostsurface of the second electrode assembly 3 b that is adjacent to thefirst electrode assembly 3 a when the rectangular secondary battery 20is completed. A second tape 80 b is attached to both the secondoutermost separator 90 b and the positive-electrode tabs 4 d that formthe second positive-electrode tab group 40 b. The second tape 80 b maybe attached either before or after the first negative-electrode tabgroup 50 a and the second negative-electrode tab group 50 b areconnected to the second negative-electrode current collector 8 b.

The second positive-electrode current collector 6 b includes a thinportion 6 c, which has a current-collector opening 6 d formed therein.The second positive-electrode current collector 6 b has acurrent-collector through hole 6 e located to face the electrolyticsolution introduction hole 15 in the sealing plate 2. The secondnegative-electrode current collector 8 b includes a thin portion 8 c,which has a current-collector opening 8 d formed therein.

Attachment of Components to Sealing Plate

FIG. 7 illustrates a surface of the sealing plate 2 that faces theinside of the battery and to which components are attached. Thecomponents are attached to the sealing plate 2 as described below.

The outer insulating member 10 is disposed on a surface of the sealingplate 2 that faces the outside of the battery in a region around thepositive-electrode-terminal-receiving hole 2 a. The inner insulatingmember 11 and the first positive-electrode current collector 6 a aredisposed on the surface of the sealing plate 2 that faces the inside ofthe battery in a region around the positive-electrode-terminal-receivinghole 2 a. The positive electrode terminal 7 is inserted through athrough hole in the outer insulating member 10, thepositive-electrode-terminal-receiving hole 2 a in the sealing plate 2, athrough hole in the inner insulating member 11, and a through hole inthe first positive-electrode current collector 6 a from the outside ofthe battery, and an end of the positive electrode terminal 7 is crimpedonto the first positive-electrode current collector 6 a. Thus, thepositive electrode terminal 7 and the first positive-electrode currentcollector 6 a are fixed to the sealing plate 2. The crimped portion ofthe positive electrode terminal 7 and the first positive-electrodecurrent collector 6 a are preferably welded to each other.

The outer insulating member 12 is disposed on the surface of the sealingplate 2 that faces the outside of the battery in a region around thenegative-electrode-terminal-receiving hole 2 b. The inner insulatingmember 13 and the first negative-electrode current collector 8 a aredisposed on the surface of the sealing plate 2 that faces the inside ofthe battery in a region around the negative-electrode-terminal-receivinghole 2 b. The negative electrode terminal 9 is inserted through athrough hole in the outer insulating member 12, thenegative-electrode-terminal-receiving hole 2 b in the sealing plate 2, athrough hole in the inner insulating member 13, and a through hole inthe first negative-electrode current collector 8 a from the outside ofthe battery, and an end of the negative electrode terminal 9 is crimpedonto the first negative-electrode current collector 8 a. Thus, thenegative electrode terminal 9 and the first negative-electrode currentcollector 8 a are fixed to the sealing plate 2. The crimped portion ofthe negative electrode terminal 9 and the first negative-electrodecurrent collector 8 a are preferably welded to each other.

The inner insulating member 11 includes an insulating member mainportion 11 a that extends along the surface of the sealing plate 2facing the inside of the battery. The insulating member main portion 11a has an insulating member opening 11 b located to face the electrolyticsolution introduction hole 15 in the sealing plate 2. A tubular portion11 c is provided around the insulating member opening 11 b. The tubularportion 11 c extends from the insulating member main portion 11 a towardthe first electrode assembly 3 a and the second electrode assembly 3 b.

Connection Between First Current Collectors and Second CurrentCollectors

FIG. 8 illustrates the surface of the sealing plate 2 facing the insideof the battery after the second positive-electrode current collector 6 bis attached to the first positive-electrode current collector 6 a andthe second negative-electrode current collector 8 b is attached to thefirst negative-electrode current collector 8 a.

The second positive-electrode current collector 6 b to which the firstpositive-electrode tab group 40 a and the second positive-electrode tabgroup 40 b are connected is placed on the inner insulating member 11 sothat the second positive-electrode current collector 6 b partiallyoverlaps the first positive-electrode current collector 6 a. Then, thethin portion 6 c is irradiated with a laser beam to join the secondpositive-electrode current collector 6 b and the firstpositive-electrode current collector 6 a together. Thus, a joinedportion 62 is formed. In addition, the second negative-electrode currentcollector 8 b to which the first negative-electrode tab group 50 a andthe second negative-electrode tab group 50 b are connected is placed onthe inner insulating member 13 so that the second negative-electrodecurrent collector 8 b partially overlaps the first negative-electrodecurrent collector 8 a. Then, the thin portion 8 c is irradiated with alaser beam to join the second negative-electrode current collector 8 band the first negative-electrode current collector 8 a together. Thus,the joined portion 63 is formed.

Assembly of Rectangular Secondary Battery

The first electrode assembly 3 a and the second electrode assembly 3 bare brought together. At this time, the first positive-electrode tabgroup 40 a and the second positive-electrode tab group 40 b are bent indifferent directions, and the first negative-electrode tab group 50 aand the second negative-electrode tab group 50 b are bent in differentdirections. The first electrode assembly 3 a and the second electrodeassembly 3 b that have been brought together are placed in the electrodeassembly holder 14, which is composed of an insulating sheet formed inthe shape of a box or a bag.

The first electrode assembly 3 a and the second electrode assembly 3 bcovered with the electrode assembly holder 14 are inserted into therectangular exterior body 1. Then, the sealing plate 2 and therectangular exterior body 1 are welded together to seal the opening inthe rectangular exterior body 1 with the sealing plate 2.

FIG. 9 is a sectional view of the sealing plate 2 taken in theshort-side direction, illustrating the region around the electrolyticsolution introduction hole 15 after the opening in the rectangularexterior body 1 is sealed by the sealing plate 2.

As illustrated in FIG. 9, the electrolytic solution introduction hole 15is disposed between the first positive-electrode tab group 40 a and thesecond positive-electrode tab group 40 b in the short-side direction ofthe sealing plate 2. The first tape 80 a and the second tape 80 b arelocated to face the electrolytic solution introduction hole 15. Asdescribed above, the first positive-electrode tab group 40 a and thesecond positive-electrode tab group 40 b are bent in differentdirections.

Electrolytic solution is introduced into the battery case 100 throughthe electrolytic solution introduction hole 15 in the sealing plate 2.The electrolytic solution may be, for example, nonaqueous electrolyticsolution obtained by dissolving electrolyte salt in an organic solvent.The electrolytic solution introduced into the battery case 100 throughthe electrolytic solution introduction hole 15 in the sealing plate 2passes through the insulating member opening 11 b, the tubular portion11 c, and the current-collector through hole 6 e, and flows toward thefirst electrode assembly 3 a and the second electrode assembly 3 b.

The first tape 80 a is attached to both the first outermost separator 90a on the outermost surface of the first electrode assembly 3 a adjacentto the second electrode assembly 3 b and the first positive-electrodetab group 40 a. The second tape 80 b is attached to both the secondoutermost separator 90 b on the outermost surface of the secondelectrode assembly 3 b adjacent to the first electrode assembly 3 a andthe second positive-electrode tab group 40 b. Therefore, the firstoutermost separator 90 a, the second outermost separator 90 b, and otherseparators 90 are prevented from being curled due to the electrolyticsolution that is introduced.

Therefore, short-circuiting between unintended portions of the positiveelectrode plates 4 and the negative electrode plates 5 due to curling ofthe first outermost separator 90 a, the second outermost separator 90 b,or other separators 90 can be prevented. In addition, falling ofportions of the positive-electrode-active-material layers 4 b and thenegative-electrode-active-material layers 5 b due to the electrolyticsolution being forcefully introduced can be reliably prevented.Accordingly, short-circuiting due to fallen portions of thepositive-electrode-active-material layers 4 b or thenegative-electrode-active-material layers 5 b can be prevented.

As illustrated in FIGS. 5 and 8, the first tape 80 a and the second tape80 b preferably have widths greater than the widths of the firstpositive-electrode tab group 40 a and the second positive-electrode tabgroup 40 b. In such a case, the first outermost separator 90 a, thesecond outermost separator 90 b, and other separators 90 can be moreeffectively prevented from curling.

The first tape 80 a and the second tape 80 b may have widths less thanthe widths of the first positive-electrode tab group 40 a and the secondpositive-electrode tab group 40 b. When a current interruption mechanismis provided on a conductive path between the first positive-electrodetab group 40 a and the positive electrode terminal 7 and between thesecond positive-electrode tab group 40 b and the positive electrodeterminal 7, the first tape 80 a and the second tape 80 b can be reliablyprevented from coming into contact with the current interruptionmechanism by setting the widths of the first tape 80 a and the secondtape 80 b less than the widths of the first positive-electrode tab group40 a and the second positive-electrode tab group 40 b. Also, when thefirst tape 80 a and the second tape 80 b have widths less than thewidths of the first positive-electrode tab group 40 a and the secondpositive-electrode tab group 40 b, the first tape 80 a and the secondtape 80 b do not come into contact with the current interruptionmechanism when being attached. Accordingly, the first tape 80 a and thesecond tape 80 b can be appropriately attached.

The length of at least one of the first tape 80 a and the second tape 80b may be increased so that at least one of the first tape 80 a and thesecond tape 80 b covers at least one of the joined portions 60. If atleast one joined portion 60 is covered with at least one of the firsttape 80 a and the second tape 80 b, even when foreign matter, such asmetal powder, is attached to the joined portion 60, the metal powder orthe like can be prevented from entering the electrode assembly 3.

The tubular portion 11 c preferably extends through thecurrent-collector through hole 6 e. An end portion (bottom end portionin FIG. 9) of the tubular portion 11 c adjacent to the first electrodeassembly 3 a and the second electrode assembly 3 b is preferably closerto the first electrode assembly 3 a and the second electrode assembly 3b (bottom side in FIG. 9) than the surface of the firstpositive-electrode tab group 40 a adjacent to the first electrodeassembly 3 a and the second electrode assembly 3 b, the firstpositive-electrode tab group 40 a being stacked on the secondpositive-electrode current collector 6 b. An end portion (bottom endportion in FIG. 9) of the tubular portion 11 c adjacent to the firstelectrode assembly 3 a and the second electrode assembly 3 b ispreferably closer to the first electrode assembly 3 a and the secondelectrode assembly 3 b (bottom side in FIG. 9) than the surface of thesecond positive-electrode tab group 40 b adjacent to the first electrodeassembly 3 a and the second electrode assembly 3 b, the secondpositive-electrode tab group 40 b being stacked on the secondpositive-electrode current collector 6 b.

After the electrolytic solution is introduced into the battery case 100through the electrolytic solution introduction hole 15 in the sealingplate 2, the electrolytic solution introduction hole 15 is sealed withthe sealing member 16, such as a blind rivet.

Tape

The tape, such as the first tape 80 a and the second tape 80 b,preferably includes a base material layer and an adhesive layer formedon the base material layer. The base material layer is preferably madeof resin. The base material layer is preferably made of a materialselected from polypropylene, polyimide, polyphenylene sulfide,polyethylene, polyester, polyethylene naphthalate, etc., or a mixturethereof. In particular, the base material layer is preferably made ofpolypropylene.

The adhesive layer is preferably adhesive at normal temperature (25°C.). The adhesive layer may be heat-weldable. The adhesive layer ispreferably made of a material selected from a rubber-based adhesive, anacrylic adhesive, a polyethylene-based adhesive, etc., or a mixturethereof. In particular, the adhesive layer is preferably made of arubber-based adhesive. The tape may be a heat-weldable sheet. In thiscase, the tape is attached by heat welding. The tape may be a glasscloth tape.

The thickness of the tape is not particularly limited, and may be, forexample, 10 μm to 500 μm.

The timing at which the tape is attached to both a tab group and aninsulating sheet is not particularly limited as long as the tape isattached before the electrolytic solution is introduced into the batterycase through the electrolytic solution introduction hole. The tape maybe attached either before or after the tab group is connected to acurrent collector.

Insulating Sheet

The insulating sheet disposed on the outermost surface of each electrodeassembly may be made of the same material as that of the separatorsdisposed between the positive electrode plates and the negativeelectrode plates. Alternatively, the insulating sheet disposed on theoutermost surface of each electrode assembly may be different from theseparators. The insulating sheet may be non-porous, but is preferablyporous so that electrolytic solution easily permeates into the electrodeassembly.

When a fan-folded separator is used, one end portion of the separatormay be wound at the outermost periphery of the electrode assembly. Theportion of the separator at the outermost periphery of the electrodeassembly may serve as the insulating sheet. Alternatively, an insulatingsheet that is separate from the fan-folded separator may be wound at theoutermost periphery of the electrode assembly.

When the electrode assembly has a wound structure, a band-shapedseparator disposed between a positive electrode plate and a negativeelectrode plate may be formed such that the separator is wound at theoutermost periphery of the electrode assembly. The portion of theseparator at the outermost periphery may serve as the insulating sheet.Alternatively, an insulating sheet that is separate from the band-shapedseparator may be wound at the outermost periphery of the electrodeassembly.

In the above-described embodiment, the positive-electrode tab groups arelocated to face the electrolytic solution introduction hole in thesealing plate. However, the negative-electrode tab groups may instead belocated to face the electrolytic solution introduction hole.

In the above-described embodiment, the first electrode assembly 3 a andthe second electrode assembly 3 b have a stacked structure. However,each of the first electrode assembly 3 a and the second electrodeassembly 3 b may instead have a wound structure. When the firstelectrode assembly 3 a and the second electrode assembly 3 b each have awound structure, the first electrode assembly 3 a and the secondelectrode assembly 3 b are each configured such that thepositive-electrode tab group and the negative-electrode tab group areprovided at an end thereof adjacent to the sealing plate 2.

In the above-described embodiment, the positive-electrode currentcollector and the negative-electrode current collector are each formedof two components. Alternatively, however, the positive-electrodecurrent collector and the negative-electrode current collector may eachbe formed of a single component. When the positive-electrode currentcollector and the negative-electrode current collector are each composedof a single component, the positive-electrode current collector and thenegative-electrode current collector are preferably respectivelyconnected to the positive electrode terminal and the negative electrodeterminal attached to the sealing plate after the positive-electrode tabgroup and the negative-electrode tab group are respectively connected tothe positive-electrode current collector and the negative-electrodecurrent collector.

In plan view of each electrode assembly that is flat, the tape may beattached to the insulating sheet on the outermost surface of theelectrode assembly such that the tape does not overlap thepositive-electrode-active-material layer. In such a case, the electrodeassembly can be prevented from receiving a large local pressure.

The positive electrode plates, the negative electrode plates, theseparators, the electrolyte, etc. may be composed of known materials.

While detailed embodiments have been used to illustrate the presentinvention, to those skilled in the art, however, it will be apparentfrom the foregoing disclosure that various changes and modifications canbe made therein without departing from the spirit and scope of theinvention. Furthermore, the foregoing description of the embodimentsaccording to the present invention is provided for illustration only,and is not intended to limit the invention.

What is claimed is:
 1. A secondary battery comprising: a first electrodeassembly including a positive electrode plate and a negative electrodeplate; a second electrode assembly including a positive electrode plateand a negative electrode plate; an exterior body having an opening andcontaining the first electrode assembly and the second electrodeassembly; a sealing plate sealing the opening; a current collector thatis closer to the sealing plate than are the first electrode assembly andthe second electrode assembly; and a terminal electrically connected tothe current collector and attached to the sealing plate, wherein thesealing plate has an electrolytic solution introduction hole, whereinthe first electrode assembly includes a first insulating sheet on anoutermost surface thereof adjacent to the second electrode assembly,wherein the second electrode assembly includes a second insulating sheeton an outermost surface thereof adjacent to the first electrodeassembly, wherein the first electrode assembly includes a firstelectrode tab group at an end thereof adjacent to the sealing plate, thefirst electrode tab group being electrically connected to the positiveelectrode plate or the negative electrode plate, wherein the secondelectrode assembly includes a second electrode tab group at an endthereof adjacent to the sealing plate, the second electrode tab groupbeing electrically connected to the positive electrode plate or thenegative electrode plate, wherein the first electrode tab group and thesecond electrode tab group are connected to the current collector,wherein a first tape is attached to both an outermost surface of thefirst tab group and the first insulating sheet, wherein a second tape isattached to both an outermost surface of the second tab group and thesecond insulating sheet, wherein at least one of the first tape and thesecond tape is located to face the electrolytic solution introductionhole, and wherein the electrolytic solution introduction hole is sealedby a sealing member.
 2. The secondary battery according to claim 1,wherein the first insulating sheet is a porous sheet, and wherein thesecond insulating sheet is a porous sheet.
 3. The secondary batteryaccording to claim 1, wherein the first electrode assembly is a stackedelectrode assembly including a plurality of the positive electrodeplates and a plurality of the negative electrode plates, and wherein thesecond electrode assembly is a stacked electrode assembly including aplurality of the positive electrode plates and a plurality of thenegative electrode plates.
 4. The secondary battery according to claim1, further comprising: an insulating member disposed on a side of thesealing plate facing an inside of the secondary battery, wherein theinsulating member has an insulating member opening located to face theelectrolytic solution introduction hole, and wherein a tubular portionis formed around the insulating member opening.
 5. The secondary batteryaccording to claim 1, wherein the current collector has acurrent-collector through hole located to face the electrolytic solutionintroduction hole.